If your attic is big enough, and has enough entry points, you can have both living up there, I see it all the time. You could even have raccoons up there at the same time! Doesn't happen often, but it happens.

You just start trapping and keep on trapping until you think you have them all. Then move the traps outside and catch some more. When you think it's enough, cover the entry points with cardboard and if they don't go in anymore, for a couple of days, screen it off temporarily. If they don't bother the screening for a couple of months, seal it the right way.